COLOMBIA, Brazil When Henrique Fiorese noticed two years ago that some of his orange trees were yellowing and losing their leaves, he thought at first that it was just another bout with a pesky crop pest called citrus variegated chlorosis. After all, that disease only causes fruit to harden and trees to wilt; it does not kill them.
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But when his trees started dying, Fiorese knew he was up against something potentially more devastating.
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This time his plants were left in a gnarl of barren branches, looking more like witch's hair than lush orange trees.
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"The damage was just brutal," recalled Fiorese, 46, who has been growing oranges on a 690-acre or 279-hectare farm in this area in northern São Paulo state for as long as he can remember. "My first thought was, 'God, I'm going to lose everything.'"
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Fiorese did not lose everything. But he has lost a lot - more than $100,000 and counting - as have hundreds of other Brazilian farmers since a mysterious new crop disease began ripping through the heart of the country's citrus belt just over three years ago.
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The disease, dubbed "citrus sudden death," is highly contagious and can kill an orange tree within weeks after the first symptoms appear. It attacks a tree's veins and eventually causes the roots to rot, cutting off the flow of water and nutrients to the rest of the plant.
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For an agricultural powerhouse like Brazil, where orange trees outnumber people, the threat posed by citrus sudden death is a serious one. Oranges are one of the country's biggest breadwinners, providing jobs for 400,000 people and bringing in a hefty $1.3 billion a year in exports. Brazil is the world's No. 1 citrus grower, with 5 out of every 10 glasses of orange juice consumed around the globe squeezed from this nation's fruit.
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The disease was first detected in early 2001 in southern part of the state of Minas Gerais and soon spilled over into groves in northern São Paulo, the state that produces almost 90 percent of Brazil's oranges for export. In just over three years, sudden death has wiped out more than 2.5 million orange trees in the region, costing growers about $40 million.
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While that is still only about 2 percent of Brazil's total citrus crop, researchers fear that nearly all the country's orange groves could be at risk. Because few citrus plantations here are irrigated, a vast majority of Brazilian orange trees are grafted to rangpur lime stalks, a root variety that is resistant to drought. But rangpur rootstocks are also especially vulnerable to sudden death, leading some experts to predict that as many as 85 percent of the country's orange trees may have to be replanted in the next six years if the disease is not kept at bay. That, in turn, could eventually mean a significant drop in citrus production in Brazil and drive up prices for frozen concentrated orange juice on world markets, something that has been avoided until now.
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"So far, we don't have enough evidence to say for sure if it's going to spread through the whole state," said Nelson Gimenes, the chief plant pathologist at Fundecitrus, a citrus research group in Araraquara.
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"But," he added, "there is also nothing that indicates that it's going to stay put. And the scary thing is that if it does spread, we're talking about almost the entire crop."
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Though its cause is still unknown, researchers believe sudden death could be a mutant form of "tristeza dos citros" - literally the citrus trees' sorrow - a deadly virus that destroyed more than 80 percent of São Paulo's orange trees in the 1940s and remains widespread in Florida's groves today. If they are right, it would be a cruel twist of fate. It was the "tristeza" outbreak that drove Brazilians to rely so heavily on the rangpur rootstock in the first place because it was the only variety that survived the epidemic.
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What is known for sure is that sudden death is transmitted by aphids, tiny insects that feed on plants and can incubate for up to three years before trees show any symptoms. That means the disease may have already spread beyond northern São Paulo and southern Minas Gerais.
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Researchers also recently discovered that the volkameriano lime, a rootstock that was originally thought to be resistant to sudden death, is in fact susceptible to it, raising the possibility that other varieties may also be at risk. Still, there may be hope for a cure now that scientists are almost certain the disease is caused by a virus, not bacteria.
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"If it's a viral disease, you can come up with a vaccine, and that's what we're trying to do," said Fernando Reinach, president of Alellyx Applied Genomics. In the meantime, growers are scrambling to protect their groves by grafting other rootstock varieties that have proven resistant to sudden death, like swingle citrumelo and cleopatra tangerine, to existing rangpur stalks.
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The process, known as inarching, helps restore the flow of nutrients through the plant and has already nursed thousands of orange trees back to life.
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The New York Times

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